An Umpolung Reaction of Aldehydes with Arynes

Significance

Biju and Glorius report an unprecedented N-heterocyclic carbene (NHC) catalyzed hydroacylation of arynes. In this umpolung reaction, various aldehydes 1 are activated via the Breslow intermediate A to react with arynes generated in situ from precursors 2. The authors propose a mechanism involving either a concerted (B) or a stepwise (C → D) addition-protonation sequence. An analogy to the more explored [2+3] cycloadditions of arynes and 1,3-dipoles is invoked for the concerted mechanism. Competition experiments provided insight into the rates of individual steps.